This invention relates to felt bands and particularly felt bands as used in the paper making industry.
The development of similar felt bands proceeded in recent years from the use of natural fibers to increasing application of synthetic fibers. The application of these fibers enabled development of new technological processes, for instance the technology of needling. The melting, or fusing together of thermoplastic fibers also belongs to these novel technological processes. The new synthetic materials provided improved resistance to abrasion, against the influences of different chemicals, moulds and similar. These materials found their application particularly in the manufacture of felt bands in paper making for dewatering, dehumidifying and drying, for manufacture of materials for filtering and insulating, and similar applications. In the case of felt bands for the manufacture of paper there are particularly needled felt bands having an internal structure where the supporting tissue or netting is connected with a needled fleece of fibers which are not feltable.
The supporting tissue in such a structure serves here as a supporting medium and as means for achievement of the required strength and stability of dimensions, whereby the loops of said supporting tissue can serve as storage spaces for the working medium, for instance water. This support, however, has some undesirable properties. New types of felt bands have therefore been developed which have few or no wefts and recently felt bands having practically no supporting tissue and represent a layer obtained by a fiber fleece reinforced by needling, have been developed. The stability of dimensions and required strength of these materials is obtained both by intensive needling and by chemical impregnation or melting together. By needling, bonds are formed in a fleece of fibers which are not feltable, which provide the strength of the fleece and which connect the individual layers of fiber fleeces together. The chemical impregnation of the felt band also provides the necessary strength and stability of dimensions. Internal bonds between thermoplastic fibers can also be created by fusing them together in order to strengthen the structure of the felt band. These felt bands are spatially arranged so that the fibers are oriented in the plane of the surface of the felt band and the bonds are oriented in a direction substantially perpendicular to this plane. In case of a chemical working of the felt band, bonds are created by bonding the fibers of the fleece with some synthetic resin in the whole structure of the felt band. Drawbacks of these methods of making felt bands are that no storage spaces for the working medium are provided and furthermore that they adversely influence some of the required properties as perviousness, strength, elasticity, clogging, etc.